Power limit registers in Sandy bridge

[Sankaralingam_P_]

Hi,

I am trying to play around with the power limit register (MSR_PP0_POWER_LIMIT) available in sandy bridge architecture. The machine is equipped with i5-2500K processors. But after modifying the register, I don't see any impact on the power consumption. I use the energy status register (MSR_PP0_ENERGY_STATUS) to measure the energy consumption and divide it by time spent to get the average power consumption. I get the same power measurement before and after I modify the power limit register.

I tried the same process with one of the Xeon processor and it seemed to work. I can notice the change in the power consumption of the cpu cores. 

Does it mean that these registers work only in server class processors and not in desktop processors ?

- Sankar

[Roman_D_Intel]

Sankar, did you try Intel(r) Power Governor for changing the PP0 limits? best regards, Roman

[Sankaralingam_P_]

Roman, Thanks for the response. I tried changing the register manually through msr registers. I came across the power governor and it seems to be able to do what I needed, but the download link in the page does not work. - Sankar

[Roman_D_Intel]

Sankar, I will report the issue with the link and let you know. Roman

[Sankaralingam_P_]

I manually try to change the msr (power limit registers) which I think is what power_gov also does. I see that the lock bit is not set in any of the power limit registers (MSR_PKG or MSR_PP0 or MSR_PP1). I modify the values in the register and made sure that changes are reflected (by reading back the register) but still I do not see any impact on the system after modifying the registers. I came across this in another thread (http://software.intel.com/en-us/forums/topic/282122) - I am not sure if the root cause is the same. If the 28th bit is set to 0 in MSR_PLATFORM_INFO (0xCE) register, I cannot write to MSR 0x1AD to change the turbo ratio. But in my case, I can write to the power limit registers. Are there any other possibilities like motherboard vendors blocking the usage of these registers? If so, is there any way to test it?

[Roman_D_Intel]

the links should work now. Let us know if it works for you

[Sankaralingam_P_]

I was able to download the tool but I was not able to resolve the original issue.